Accumulated Other Comprehensive Loss - Schedule of Changes in Accumulated Other Comprehensive Loss After Tax (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total Accumulated Other Comprehensive Income (Loss), Beginning Balance	$ (42,495)
Total other comprehensive (loss) income	(2,167)	4,588
Total Accumulated Other Comprehensive Income (Loss), Ending Balance	(44,662)
Unrealized Gains and Losses on Available for Sale (AFS) Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income before reclassifications	3,936
Amounts reclassified from other comprehensive income	(1,409)
Total other comprehensive (loss) income	2,527
Total Accumulated Other Comprehensive Income (Loss), Ending Balance	637	(1,890)
Non-Credit Impairment Losses on AFS Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income before reclassifications	(421)
Amounts reclassified from other comprehensive income	(84)
Total other comprehensive (loss) income	(505)
Total Accumulated Other Comprehensive Income (Loss), Ending Balance	(360)	145
Unrealized Gains and Losses on Derivatives [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income before reclassifications	(5,259)
Amounts reclassified from other comprehensive income	951
Total other comprehensive (loss) income	(4,308)
Total Accumulated Other Comprehensive Income (Loss), Ending Balance	(18,840)	(14,532)
Total Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income before reclassifications	(1,744)
Amounts reclassified from other comprehensive income	(423)
Total other comprehensive (loss) income	(2,167)
Total Accumulated Other Comprehensive Income (Loss), Ending Balance	(44,662)	(42,495)
Defined Benefit Pension Plan [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income before reclassifications	0
Amounts reclassified from other comprehensive income	119
Total other comprehensive (loss) income	119
Total Accumulated Other Comprehensive Income (Loss), Ending Balance	$ (26,099)	$ (26,218)